A conventional intelligent power module (IPM) sends detected signals in multiple phases on a secondary side, which is a high-voltage side, to a primary side, which is a low-voltage GND side, via a photocoupler, and selects the signals on the primary side, as appropriate.
Reference is made to temperature outputs of an IPM used for an inverter for instance. Chip temperatures of, for instance, an Insulated Gate Bipolar Transistor (IGBT) are converted into voltages as temperature signals. The temperature signals undergo Pulse Width Modulation (PWM) modulation, undergo insulation in the photocoupler, and are then transmitted from the secondary side to the primary side. The primary side demodulates the temperature signals through PWM, selects the temperature signal in one phase from among the temperature signals in all the phases, and outputs the selected temperature signal. Here, a temperature signal indicating the highest temperature among those in six phases needs to be selected in order to protect the IPM.
Patent Document 1 discloses a DC-DC converter that outputs a synchronization signal at the timing when a voltage at a secondary wire terminal rises to a secondary rectified voltage.